The invention relates generally to deposition processes, and, more particularly, to a system for monitoring various deposition parameters and effecting selective changes in these parameters to achieve a predetermined composition of deposited material.
Known equipment for producing thin-film devices by sputtering deposition techniques has not been completely satisfactory, especially where large quantity production and reproducibility is desired. This has been primarily because of past inability to monitor deposition parameters, such as substrate temperature, pressures of reactive gases, plasma composition, and the resulting microstructure of the device being deposited, with sufficient precision and rapidity to enable modification of selected parameters to achieve a predetermined composition and microstructure. Many attempts have been made in the past to determine the material composition being deposited by optical means, for example, in which the sputtering discharge of a system is monitored by a scanning spectrometer, and the light energy emitted from the plasma is thereby used to generate a signal functionally related to the composition of the deposited material. Reference is made to the article in the Journal of Vacuum Science Technology, Vol. 10, No. 6, November/December 1973, entitled Glow Discharge Optical Spectroscopy for Monitoring Sputter Deposited Film Thickness by J. E. Greene and F. Sequeda-Osorio.
In U.S. Pat. No. 3,738,926, METHOD AND APPARATUS FOR CONTROLLING THE ELECTRICAL PROPERTIES OF SPUTTERED FILMS, by W. D. Westwood and R. J. Boynton, two wavelengths of light emitted by the plasma are optically monitored, the intensities of which have been found to be related to the film electrical properties.
None of the known prior optical approaches provide a closed-loop control for sputtering deposition equipment to achieve high quantity production of films of predetermined characteristics.
In an article in the Journal of Aplied Physics, Vol. 44, No. 6, pages 2610-2618, June, 1973, W. D. Westwood and R. J. Boynton described mass spectrometric analysis of sputtering discharge; however, the analysis is concerned with the composition of the gases outside the discharge rather than the directly sputtered species in the discharge.